After all, they were in the forest not to sightsee but to make money — lots of it.

Jeff Seefeldt, district ranger for the U.S. Forest Service, surveyed the scene with disgust.

“When the spring rains come all this would have ended up in that Class A trout stream,” Seefeldt said nodding to the south branch of the Oconto River that wound through an area that had been clear cut and planted with hundreds of marijuana plants.

Heavily armed drug traffickers from Mexico are using the only national forest in Wisconsin as their personal farms and greenhouses, growing millions of dollars in marijuana and leaving behind their garbage, poached deer carcasses, and fertilizer and pesticides.

For the last three summers, large marijuana operations have been discovered in the Chequamegon-Nicolet National Forest in northern Wisconsin. In each of those busts, law enforcement made numerous arrests, almost all natives of Mexico here illegally. Confiscated weapons included handguns, AK-47s and a .308-caliber rifle with ammunition magazines taped together.

Since 2008 officers have discovered 11 large illegal marijuana operations, mostly on public land in Wisconsin.

Investigators say it’s likely only the tip of the iceberg.

Each of the last three major grows in the Chequamegon-Nicolet were discovered by hunters or anglers. With 1.5 million acres of remote land in the national forest, and many more millions of acres in county and state land, law enforcement is trying to get the word out to outdoors enthusiasts. That includes more than 600,000 hunters heading into the woods for opening weekend of the gun-deer season Saturday.

In the back page of this season’s deer hunting regulations pamphlet, hunters are cautioned to be suspicious of illegal drug operations on public land and leave immediately when they see areas with abnormal cuttings or clearings, makeshift structures, gardening tools, watering cans and chemical containers. Hunters who see something that doesn’t look right should note the location, with GPS coordinates if possible, and report it to law enforcement.

“It’s a significant problem,” said Wisconsin Attorney General J.B. Van Hollen. “We have people who want to use our lands for public recreation and they’re at risk from people who have a big cash crop to protect. When we encounter ammunition and people armed in the woods with that incentive, it’s a great danger to the public.”

Of those arrested in the last few years, many revealed they were recruited in California for the work, driven to northern Wisconsin — some didn’t even know which state they were in — and dropped off in the woods. They were supplied by people dubbed “loncheros” who stopped every few days to bring supplies.

While the 2012 case is pending, 10-year federal prison sentences were handed down in the other cases. After they serve their prison terms, they will be deported back to Mexico.

“Which begs the question why do we bother if we’re going to deport?” said U.S. Attorney John Vaudreuil for the Western District of Wisconsin.

“But I have a strong feeling that that’s not right. If this was an American citizen doing this crime they would serve 10 years. Plus there’s a good chance the guys will come back to the U.S. and do this again if we deport them right away,” said Vaudreuil.

Using hand axes and saws they cut down thousands of trees, clear cut numerous small areas of the forest, planted marijuana and then carefully cultivated the plants each day by siphoning water from nearby streams before harvesting and packing it out where it likely ended up being sold in Milwaukee, Detroit, Chicago and the Twin Cities.

Why are Mexican drug organizations coming all the way to Wisconsin when they can grow marijuana out west? Economics, explained David Spakowicz, state Division of Criminal Investigation director of field operations for Wisconsin’s eastern region.

“Once it’s up in northern Wisconsin, you don’t have to worry about transportation costs, you don’t have to worry about getting it over the (U.S.-Mexico) border. It’s so appealing because of the rural nature of Wisconsin,” Spakowicz said.

It’s also a labor intensive crop if done right. Marijuana plants are cultivated by breaking off the leaves, which pushes the tetrahydrocannabinol, or THC, to the bud and makes the weed more potent and valuable. High-grade marijuana found growing on public land in California has a street value of $4,000 to $6,000 per pound, Spakowicz said.

He estimated much of the marijuana found in recent years on public land in Wisconsin would have a street value of $2,500 per pound. Each marijuana plant provides roughly 1 pound of pot. Last summer in the Chequamegon-Nicolet in Oconto County 8,385 plants were confiscated while almost 7,000 plants were discovered in the forest in Ashland County in 2011.

The plants are dried on racks made from poles cut and lashed together, then usually vacuumed packed into plastic bags and carried out where the men and their backpacks filled with marijuana are picked up and driven away, leaving behind their garbage and hundreds of holes left in the ground. Investigators know in some cases growers returned to use the same land in subsequent years when they were not detected.

“It disgusts me. They don’t respect the environment, they don’t respect other people who want to enjoy the land,” said Seefeldt, who grew up in Wausau. “I would think there would be a huge outcry from the public because these people are misusing the land.”

Since Wisconsin has a shorter growing season than in western states, growers usually plant two crops, putting three to four seedlings in each hole. The seedlings are typically planted in May and then another crop is planted a couple weeks later so the first crop is ready for harvesting in late August and the second crop can be picked before the first frost arrives.

Growers pick their areas for remoteness and access to water, cutting down trees to reduce the canopy and allow in more light, which sometimes raises the temperature of trout streams. Law enforcement has found stumps covered with dirt so they won’t be noticed in aerial surveillance. At one site investigators discovered a 4-foot-deep pit where growers hid their generators, water pumps and cellphone chargers with logs and a tarp over the top to reduce noise.

As more sites have been discovered and arrests made, officers noticed growers changed their tactics, planting in more remote areas and dividing their crop up into smaller quarter- to half-acre plots. Wisconsin National Guard helicopters were used at one site to airlift the garbage and marijuana plants out of a remote area.

National, state and county forest land is used because it is less likely to be detected, Spakowicz said.

“With these vast tracts of public land they sort of roll the dice; that’s why they go so far in to the woods,” Spakowicz said. “They’re living there for three months and they’re very knowledgeable about the terrain.”